SIDR G. Huston
Internet-Draft APNIC
Intended status: Standards Track S. Weiler
Expires: October 15, 2011 SPARTA, Inc.
G. Michaelson
APNIC
S. Kent
BBN
April 13, 2011
Resource Certificate PKI (RPKI) Trust Anchor Locatordraft-ietf-sidr-ta-07
Abstract
This document defines a Trust Anchor Locator (TAL) for the Resource
Certificate Public Key Infrastructure (RPKI).
Status of this Memo
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This Internet-Draft will expire on October 15, 2011.
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Internet-Draft RPKI Trust Anchor Locator April 20111. Introduction
This document defines a Trust Anchor Locator (TAL) for the Resource
Certificate Public Key Infrastructure (RPKI) [ID.sidr-arch]. This
format may be used to distribute trust anchor material using a mix of
out-of-band and online means. Procedures used by relying parties
(RPs) to verify RPKI signed objects SHOULD support this format to
facilitate interoperability between creators of Trust Anchor (TA)
material and RPs.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
2. Trust Anchor Locator2.1. Trust Anchor Locator Format
This document does not propose a new format for TA material. A TA in
the RPKI is represented by a self-signed X.509 CA certificate, a
format commonly used in PKIs and widely supported by RP software.
This document specifies a format for data used to retrieve and verify
the authenticity of a TA, in a very simple fashion. That data is
referred to as "Trust Anchor Locator" (TAL).
The motivation for defining the TAL is to enable selected data in the
trust anchor to change, without needing to effect re-distribution of
the trust anchor per se. In the RPKI, certificates contain
extensions that represent Internet Number Resources (INRs) [RFC3779].
The set of INRs associated with an entity likely will change over
time. Thus, if one were to use the common PKI convention of
distributing a TA to RPs in a secure fashion, this procedure would
need to be repeated whenever the INR set for the TA changed. By
distributing the TAL (in a secure fashion), instead of the TA, this
problem is avoided, i.e., the TAL is constant so long as the TA's
public key and its location does not change.
The TAL is analogous to the TrustAnchorInfo data structure adopted as
a PKIX standard [RFC5914]. That standard could be used to represent
the TAL, if one defined an rsync URI extension for that data
structure. However, the TAL format was adopted by RPKI implementors
prior to the PKIX TA work, and the RPKI implementer community has
elected to utilize the TAL format, rather than define the requisite
extension. The community also prefers the simplicity of the ASCII
encoding of the TAL, vs. the binary (ASN.1) encoding for
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Internet-Draft RPKI Trust Anchor Locator April 2011
TrustAnchorInfo.
The TAL is an ordered sequence of a rsync URI [RFC5781], and a base
64-encoding with URL and filename safe alphabet [RFC4648], DER-
encoded X.509 [X.509] subjectPublicKeyInfo [RFC5280]. The sequence
separator is an ASCII line break sequence, namely the CR LF character
pair. The CR character is OPTIONAL.
2.2. TAL and Trust Anchor Certificate Considerations
The rsync URI in the TAL MUST reference a single object. It MUST NOT
reference a directory or any other form of collection of objects.
The referenced object MUST be a self-signed CA certificate that
conforms to the RPKI certificate profile [ID.sidr-res-certs]. This
certificate is the trust anchor in certification path discovery
[RFC4158] and validation [RFC5280][RFC3779].
The validity interval of this trust anchor SHOULD reflect the
anticipated period of stability the particular set of Internet Number
Resources (INRs) that are associated with the putative TA.
The INR [RFC3779] extension(s) of this trust anchor MUST contain a
non-empty set of number resources. It MUST NOT use the "inherit"
form of the INR extension(s). The INR set described in this
certificate is the set of number resources for which the issuing
entity is offering itself as a putative trust anchor in the RPKI
[ID.sidr-arch].
The public key used to verify the trust anchor MUST be the same as
the subjectPublicKeyInfo in the CA certificate and in the TAL.
The trust anchor MUST contain a stable key. This key MUST NOT change
when the certificate is reissued due to changes in the INR
extension(s), when the certificate is renewed prior to expiration or
for any reason other than a key change.
Because the public key in the TAL and the trust anchor MUST be
stable, this motivates operation of that CA in an off-line mode.
Thus the entity that issues the trust anchor SHOULD issue a
subordinate CA certificate that contains the same INRs (via the use
of the "inherit" option in the INR extensions of the subordinate
certificate). This allows the entity that issues the trust anchor to
keep the corresponding private key of this certificate off-line,
while issuing all relevant child certificates under the immediate
subordinate CA. This measure also allows the CRL issued by that
entity to be used to revoke the subordinate (CA) certificate in the
event of suspected key compromise of this potentially more vulnerable
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Internet-Draft RPKI Trust Anchor Locator April 2011
online operational key pair.
The trust anchor MUST be published at a stable URI. When the trust
anchor is re-issued for any reason, the replacement CA certificate
MUST be accessible using the same URI.
Becuase the trust anchor is a self-signed certificate, there is no
corresponding Certificate Revocation List that can be used to revoke
it, nor is there a manifest [ID.sidr-rpki-manifests] that lists this
certificate.
If an entity wishes to withdraw a self-signed CA certificate as a
putative Trust Anchor, for any reason, including key rollover, the
entity MUST remove the object from the location referenced in the
TAL.
2.3. Example
rsync://rpki.example.org/rpki/hedgehog/root.cer
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAovWQL2lh6knDx
GUG5hbtCXvvh4AOzjhDkSHlj22gn/1oiM9IeDATIwP44vhQ6L/xvuk7W6
Kfa5ygmqQ+xOZOwTWPcrUbqaQyPNxokuivzyvqVZVDecOEqs78q58mSp9
nbtxmLRW7B67SJCBSzfa5XpVyXYEgYAjkk3fpmefU+AcxtxvvHB5OVPIa
BfPcs80ICMgHQX+fphvute9XLxjfJKJWkhZqZ0v7pZm2uhkcPx1PMGcrG
ee0WSDC3fr3erLueagpiLsFjwwpX6F+Ms8vqz45H+DKmYKvPSstZjCCq9
aJ0qANT9OtnfSDOS+aLRPjZryCNyvvBHxZXqj5YCGKtwIDAQAB
3. Relying Party Use
In order to use the TAL to retrieve and validate a (putative) TA, an
RP SHOULD:
1. Retrieve the object referenced by the URI contained in the TAL.
2. Confirm that the retrieved object is a current, self-signed RPKI
CA certificate that conforms to the profile as specified in
[ID.sidr-res-certs].
3. Confirm that the public key in the TAL matches the public key in
the retrieved object.
4. Perform other checks, as deemed appropriate (locally), to ensure
that the RP is willing to accept the entity publishing this self-
signed CA certificate to be a trust anchor, relating to the
validity of attestations made in the context of the RPKI
(relating to all resources described in the INR extension of this
certificate).
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Internet-Draft RPKI Trust Anchor Locator April 2011
An RP SHOULD perform these functions for each instance of TAL that it
is holding for this purpose every time the RP performs a re-
synchronization across the local repository cache. In any case, an
RP also SHOULD perform these functions prior to the expiration of the
locally cached copy of the retrieved trust anchor referenced by the
TAL.
4. Security Considerations
Compromise of a trust anchor private key permits unauthorized parties
to masquerade as a trust anchor, with potentially severe
consequences. Reliance on an inappropriate or incorrect trust anchor
has similar potentially severe consequences.
This trust anchor locator does not directly provide a list of
resources covered by the referenced self-signed CA certificate.
Instead, the RP is referred to the TA itself and the INR extension(s)
within this certificate. This provides necessary operational
flexibility, but it also allows the certificate issuer to claim to be
authoritative for any resource. Relying parties should either have
great confidence in the issuers of such certificates that they are
configuring as trust anchors, or they should issue their own self-
signed certificate as a trust anchor and, in doing so, impose
constraints on the subordinate certificates. For more information on
this approach, see [ID.reynolds-rpki-ltamgmt].
5. IANA Considerations
[This document specifies no IANA actions.]
6. Acknowledgments
This approach to TA material was originally described by Robert
Kisteleki.
The authors acknowledge the contributions of Rob Austein and Randy
Bush, who assisted with earlier versions of this document and with
helpful review comments.
7. ReferencesHuston, et al. Expires October 15, 2011 [Page 6]